iPhone and iPad exceeding shared Screen Time limits without parental approval

Hi. My child is regularly exceeding her Apple screen time limits. I have the settings on to block at end of limit, and I know it works sometimes because she has to send screen time requests. I also get a notification if the screentime passcode is typed on her device when I enter it for her (she doesn't know the code). But, regularly when I check her screen time, I see 2 apps, snapchat and roblox that together have exceeded her total time limit, without me giving her extra screen time. She does have 2 devices, an iphone and an iPad, but i have the share across devices switched on. Any ideas?

[Re-Titled by Moderator]

Original Title: Child exceeding ScreenTime limits